Post here news and photos and all other items related to Uranus and Neptune.

Here are recent infrared images acquired by the Keck II telescope at the Mauna Kea Observatories show more detail in the Uranian atmosphere than has ever been revealed before, even more detailed than anything taken by Voyager 2 or Hubble.

The bright blue arc on the left side of the planet is in fact due to one of Uranus' rings, not an atmospheric feature.

I read something about a possible orbiter mission in Cassini's style for Uranus (sadly it is highly unlikely we'll see anything orbiting Neptune before we see humans walk on Mars), which is being considered by NASA, although not approved yet. I do hope this mission actually happens; both planets interest me quite a lot.

That's a bummer. It would be great to find out new things about these planets. Why their magnetic fields are different to their polar tilt. Why Uranus is tilted like it is in the first place. Exactly how many moons does each planet have.

So many things that they could find out but it may not happen any time soon.

Actually, we (believe) we know this already -- because of giant collisions between proto-planets late in the formative phases of the solar system. The leading explanation for the origin of Earth's moon is from a glancing collision with a Mars-sized object, Mercury got stripped of its crust from a massive collision, and many of the other bodies in the solar system show evidence of being subjected to such collisions as well. So it makes sense that this would explain the distribution of axial tilts among planets, particularly Uranus.

I would like to add that recent simulations suggest that it could also have been a head-on collision between two similarly sized objects (4-5 Mars masses each). Less intuitive than the glancing blow between different sized objects, but according to the simulations it's quite possible.

If it was a collision though, wouldn't it have exploded and pushed all the gas material away from Uranus?

I have a theory and it is probably a very stupid one but I think that Uranus was tilted onto it's side when Neptune and Uranus swapped orbits. The magnetic field and gravity from Neptune (and to an extent Saturn and Jupiter) pulled at the magnetic poles which (after being pulled far enough off it polar rotation) then turned the planet on it's side. Even Neptune's magnetic poles are not the same as it's tilt (which is quite tilted itself but Saturn and Jupiter were further away and that's why it isn't completely on it's side).

It is just hard to imagine that a collision like that would leave the planet being that large. I could be wrong but I was trying to think of another possible reason.

Well, perhaps the collision happened quite early and there was still gas Uranus could collect with its gravity? Or perhaps Uranus was originally bigger, like Saturn, and most of it did indeed blow off? In any case, If I remember correctly Uranus and Neptune actually contain quite low amounts of gas and are quite different from Jupiter and Saturn. They have about 1 Earth mass of hydrogen and helium and it forms their atmosphere. Under that is essentially a really big Oceania of fourteen Earth masses. At least, that's what I remember; it could be wrong. At any rate, it seems unlikely the magnetic fields would have something to do with it; it seems unlikely they could ever be strong enough to tilt the planet.

it seems unlikely the magnetic fields would have something to do with it; it seems unlikely they could ever be strong enough to tilt the planet.

I'm just trying to think of other possibilities, that's all.

I think that with the tug from both planets magnetic fields and their gravity, it could be possible. Add to that, the slight tugs of gravity from Saturn and Jupiter and that could help the process. It could also explain why the magnetic fields on both planets are "off center" from the polar rotation as well. If Neptune has the stronger magnetic field and stronger gravity, that could also be the reason why it didn't tilt as much and Uranus ended up on it's side.

Like I said though, it's just a personal theory because I just don't think that 2 bodies of that size could collide and survive the impact.

Well, the size is all the more reason they should survive (well, one should survive; the impactor didn't, after all). The greater total mass means a huge escape velocity. If two little asteroids collided at huge speeds, their gravel would probably be spread over the solar system, but if Jupiter and Saturn crashed into each other at the same speed, the result would be messy, but it would result in a single 1.3 Jupiter mass gas giant. Some of the gas and rubble would escape, sure, but 99% of it would surely never reach escape velocity for such a huge mass. The same likely applies for Uranus.

The angle of collision would have to be a major factor for that to happen though, just like with our moon.

Could that happen twice or possibly 3 times in the same solar system? Having the impact at just the right angle for things to work out exactly how they did? (including the theory that Venus was flipped upside down due to something similar happening)

I just think gravity has a stronger input than some people give it credit for.

It could also explain why the magnetic fields on both planets are "off center" from the polar rotation as well.

Magnetic field on Uranus and Neptune is generated in relatively thin layer of salt "water" (actually, ,mixture of water, ammonia and methane), which surrounding the giant solid core (while on Earth, Jupiter and Saturn - vise versa, thick conductive layer surrounds a small solid core). This configuration cannot generate symmetrical dipole field, so Uranus' and Neptune's magnetic fields have significant quadrupole and higher momentums (thinking of planetary magnetic field as simply "North" and "South" poles is quite primitive, slightly correlates with reality).

Anyway, magnetic forces is too weak, they cannot change rotation axis of the planet, especially during single close encounter, when Uranus and Neptune exchanges their orbits. The energy, required for pushing Uranus by 90 degrees, is enormous - about 2*1035 Joules. It's equal to energy that Sun emitted during 16.5 years!

Quote (DaninAus)

Like I said though, it's just a personal theory because I just don't think that 2 bodies of that size could collide and survive the impact.

They could. All depends on relative velocity. Primitive calculation is this: collision energy (or kinetic energy of both bodies in their common center mass reference system) should not exceed the gravitational energy of both bodies or new body that will form (it is the energy that you should apply to destroy the planet - blow out all it's material to infinity).

I just think gravity has a stronger input than some people give it credit for.

And no, gravity can't rotate planet, because planet is almost spherically symmetrical. The tidal forces that acts on equatorial "bulge" is too weak compared to planet's rotating energy. Gravity can only force planetary axis to wiggle - this is called "precession".

However, self-rotation of axis can be caused by Dzhanibekov effect. This may be the cause why Mars changed its axis by 90° several times in its history. But Uranus obviously changed its axis last time until its formation was complete - because it have a regular system of satellites that orbiting in its equatorial plane.